Effects of Dietary Glutamine Supplementation on Heat-Induced Oxidative Stress in Broiler Chickens: A Systematic Review and Meta-Analysis

Antioxidants

Feb 2023

DOI: 10.3390/antiox12030570

Citations:21

Influential Citations:0

Systematic Reviews / Meta-Analyses

Enhanced Details

Methods

In vivo broiler chicken trials under heat stress (acute, cyclic, chronic). 13 English-language peer-reviewed studies (2009–2020) examined dietary glutamine supplementation. Breeds included Arbor Acres and Ross 308; sexes varied; HS models and designs varied; outcomes included growth performance and antioxidant biomarkers; meta-analysis used fixed- or random-effects models depending on heterogeneity; risk of bias assessed with SYRCLE.

Results

Glutamine supplementation under heat stress improved growth performance and antioxidant status in broilers. Growth: BWG increased (SMD 0.70; 95% CI 0.50–0.90; p<0.05); FI increased (SMD 0.64; 95% CI 0.43–0.86; p<0.05); FCR decreased (MD −0.05; 95% CI −0.07 to −0.02; p<0.05). Tissue GLN increased (overall SMD 1.21; 95% CI 1.00–1.43). Antioxidants: GPX (overall SMD 1.12), SOD (0.97), CAT (0.94), GSH (1.25) all increased; MDA decreased (overall SMD −0.84; 95% CI −1.33 to −0.35; p<0.01). Serum GPX increase was variable (SMD 0.45; 95% CI −0.63 to 1.52; p=0.41) with high heterogeneity. Longer HS duration reduced FI, GPX, and SOD; higher dietary glutamine concentration (about 1% increments) associated with higher GPX and SOD. Conclusion: dietary glutamine can mitigate HS by enhancing antioxidant defenses and growth in broilers, with stronger effects under short-term HS; tissue responses vary; dose–response trends suggest higher glutamine may further boost GPX and SOD; caution due to heterogeneity and biases; more dose–response research is needed.

Limitations

Moderate-to-high heterogeneity across studies; tissue-specific responses and measurement variability; variation in HS models and glutamine dosing; potential biases in several domains (randomization, housing, blinding, outcome assessment); English-language only; limited to Arbor Acres and Ross 308 strains; 13 studies; most conducted in China; not all endpoints measured consistently; no standardized dosing guidelines.

Abstract

In avian species, heat stress (HS) is usually the result of being exposed to high ambient temperatures, whereas oxidative stress (OS) results from the overproduction of reactive oxygen species. The current literature suggests that HS often leads to OS. Therefore, this systematic review and meta-analysis was conducted to assess the effects of dietary supplementation of glutamine on the antioxidant status and growth performances in heat-stressed broilers. A total of 13 studies were deemed eligible after an exhaustive search of the literature from Google Scholar, PubMed, and Scopus. Briefly, the following criteria were used to select the studies: trials performed on broilers; publication in peer-review journals using English as the text language; and sufficient details about the design and inclusion of dietary glutamine as a treatment for HS. Two main categories of outcomes were extracted from the studies included in the review: growth parameters and OS markers. For the meta-analysis, a random effect model was used when the heterogeneity was higher than 50%, and a fixed effect model was applied otherwise. Pooled standardized mean differences (SMD), and mean differences (MD) with their confidence intervals (CI) from the studies revealed that dietary glutamine could increase body weight gain (SMD = 0.70, CI = 0.50 to 0.90, p < 0.05), and feed intake (FI) (SMD = 0.64, CI = 0.43 to 0.86, p < 0.05), and reduce the feed conversion ratio (MD = −0.05, CI = −0.07 to −0.02, p < 0.05) in heat-exposed birds. Additionally, higher glutamine (SMD = 1.21, CI = 1.00 to 1.43, p < 0.05), glutathione (SMD = 1.25, CI = 0.88 to 1.62, p < 0.05), superoxide dismutase (SOD) (SMD = 0.97, CI = 0.58 to 1.36, p < 0.05), and catalase (SMD = 0.94, CI = 0.72 to 1.16, p < 0.05) levels were recorded in the serum, breast, and thigh muscle after supplementation of glutamine. Furthermore, the subgroup analysis revealed that malondialdehydes levels were decreased only in the serum (SMD = −0.83, CI = −1.25 to −0.41, p < 0.001) and thigh muscle (SMD = −1.30, CI = −1.86 to −0.35, p < 0.001) while glutathione peroxidase (GPX) activity was increased in the breast (SMD = 1.32, CI = 0.95 to 1.68, p < 0.05) and thigh muscle (SMD = 1.53, CI = 1.06 to 1.99, p < 0.05). Meta-regression models indicated that longer periods of heat exposure were inversely associated with the effectiveness of dietary glutamine in increasing FI, GPX, and SOD (p < 0.05). Besides, increasing the dietary concentration of glutamine led to higher GPX and SOD levels (p < 0.05). Taken together, results suggest that dietary supplementation of glutamine can effectively mitigate the deleterious effects of HS by enhancing the antioxidant status and increasing growth performances in broilers. show less